1. Field of the Invention
The present invention relates to an inkjet printing apparatus, and more particularly, to a printing method for suppressing density unevenness due to the differing properties of ink inside an ink channel depending on the position inside the channel in a joined head made up of multiple chips joined together.
2. Description of the Related Art
In order to improve manufacturing yield, an inkjet print head may be configured as an elongated print head in which comparatively short chips with multiple printing elements laid out thereon are joined together in the printing element arranging direction. In this case, in order to keep defects such as white streaks caused by chip misalignments from appearing in an image, the individual chips are typically disposed with alternating differences in a direction intersecting the arranging direction, while providing a predetermined overlapping portion (joining portion) between the individual chips in the arranging direction. Also, in order to print a continuous 1-pixel line in the print medium conveying direction distributed across multiple printing elements, a print head arrayed with multiple printing element arrays for ejecting the same ink in the conveying direction is also provided.
FIG. 1 is a diagram illustrating an example of a joined head configured in this way. Multiple chips 130 are disposed continuously in the X direction on a base plate 120 while providing a joining portion 199 of predetermined size, with the chips 130 being alternately shifted in the Y direction so as to straddle a center line 1200 extending in the X direction.
FIG. 2 is a diagram illustrating the path of an ink channel for sharing ink among multiple chips 130. The ink channel 190 is provided on the base plate 120 while curving in a zigzag manner as illustrated in FIG. 2, and guides ink received from an ink supply port 170 to an ink discharge port 171 while supplying ink to each of the multiple chips 130 successively and in series. In the individual chips 130, supplied ink is ejected from individual printing elements in accordance with print data received from a printing apparatus.
Forming the ink channel 190 in a zigzag pattern in this way increases the adhesion area with the laminar base plate 120, and has the effect of ensuring adhesion strength. However, there are also concerns that the ink flow rate decreases near the individual turns compared to the other areas. In addition, in the areas 1100 where the ink flow rate decreases in this way, ink properties such as temperature and concentration as well as the quantity of discharged ink change with respect to the other areas, and results in noticeably density unevenness in an image in some cases.
Japanese Patent Laid-Open No. H05-057965 (1993) discloses a configuration for avoiding noticeable discontinuities in an image at the joining portions of a joined head, in which a number of the printing elements that actually conduct ejection operations are gradually increased from the end of the chips and proceeding inwards, even in the same joining portion. If Japanese Patent Laid-Open No. H05-057965 (1993) is implemented, even if the ink properties change in the low flow rate areas 1100 of the channel, such areas are almost entirely contained within the joining portions, thus making it possible to reduce the number of ejections by printing elements included in the low flow rate areas 1100, and suppress image defects such as density unevenness.
However, the configuration of Japanese Patent Laid-Open No. H05-057965 (1993) gradually increases the number of printing elements used for actual ejection from the edge towards the center. Thus, several printing elements are used for ejection operations even though the printing elements are included in the low flow rate areas 1100, and ink droplets with different densities and ejection amounts are unavoidably ejected to some degree.
Also, in the case of a joined head configured as in FIG. 1, since the low flow rate areas 1100 appear at the turns of the ink channel 190 as illustrated in FIG. 2, the numbers of printing elements included in the low flow rate areas 1100 differ by the individual printing element arrays. However, since Japanese Patent Laid-Open No. H05-057965 (1993) is proposed for the case where there is basically one array of printing elements each laid out on the individual chips, no consideration is predetermined for the ejection properties between printing element arrays in the case of laying out multiple printing element arrays on the individual chips as in FIG. 1.